Wellbore Casing Cutting Tool

ABSTRACT

A wellbore casing cutting tool, having multiple blades which rotate outwardly by a fluid operated mechanism, has multiple cutters on each blade. The cutters are preferably positioned on the blades such that the lowermost cutting edges of multiple cutters all bear on the surface of the casing being cut. The cutters are preferably made with a metal base, covered with hardened cutting material such as tungsten carbide or hardened cutting buttons. The metal wears away as cutting progresses, continually exposing fresh cutting surfaces. The multiple cutters permit cutting of long windows in casing walls, and the structure of the cutters results in relatively short metal cuttings, rather than long metal cuttings which can ball up downhole.

CROSS REFERENCE TO RELATED APPLICATIONS

This Patent Application claims priority to U.S. provisional patent application Ser. No. 61/542,991, filed Oct. 4, 2011, for all purposes.

BACKGROUND

Various tools have been developed for downhole cutting or severing of casing strings in wellbores, and for cutting or milling window sections in casing strings. Generally, such tools have comprised a main body with multiple hinged arms or blades, which are rotated outwardly into contact with the casing (by hydraulic or other means) when the tool is in position downhole. Usually, fluid is pumped down through the drillstring and through the tool to actuate the mechanism and rotate the blades outward. Once the blades are rotated outwardly, rotation of the drillstring (and tool) causes the cutting surfaces on the blades to cut through the casing string. Fluids are pumped through the system to lift the cuttings to the surface. Known tools, however, cannot efficiently cut or sever multiple, cemented-together casing strings, and in particular cannot efficiently cut “windows” in such strings; by the term “window” is meant the cutting or milling of a section (e.g. 20′) of the casing string, as opposed to simply severing same. In addition, known tools tend to form long, connected metal shavings which must be lifted from the wellbore by the fluid flow, else same become nested together downhole and potentially cause the drillstring to become stuck.

SUMMARY OF THE INVENTION

A wellbore casing cutting tool having multiple rotatably mounted blades comprises, in a preferred embodiment, multiple cutters mounted on or integral to each blade. The cutters are preferably positioned in a row such that the lowermost cutting edges of multiple cutters are substantially aligned, so that the multiple cutters all bear on the surface of the casing being cut. The cutters are preferably made with a metal base, preferably somewhat softer than the casing being cut, having hardened cutting surfaces covering the metal (such as a carbide coating), or having a plurality of hard cutting buttons mounted on the blade. The metal wears away as cutting progresses, continually exposing fresh cutting surfaces. The multiple cutters and their shape and configuration permit lengthy cutting periods without removal of the tool from the wellbore, thereby permitting the cutting of long windows in casing walls in a single trip. Further, the nature of the cutters results in relatively short metal cuttings from the casing being cut, rather than long metal cuttings which can ball up downhole.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side view in partial cutaway of an exemplary tool embodying the principles of the present invention.

FIG. 2, which is divided into FIGS. 2A thru 2G, has further detail regarding one embodiment of a blade with cutters attached, and detail regarding the blade configuration.

FIG. 3 is a cutaway top view, looking downwardly along the longitudinal axis of the tool.

FIG. 4 is a side view showing position of the cutters as they move along a surface of casing being cut or milled.

FIG. 5 is another side view showing position of the cutters as they move along a surface edge of casing being cut or milled, viewed from a position roughly 90 degrees around the circumference from the view of FIG. 4.

FIG. 6 shows additional attributes of a preferred embodiment of the cutters.

FIG. 7 shows an alternative embodiment of the cutters.

FIGS. 8 and 9 show an alternative embodiment of a blade and cutter. FIG. 9 is a view in the direction of the arrow shown in FIG. 8.

DESCRIPTION OF THE PRESENTLY PREFERRED EMBODIMENT(S)

While a number of embodiments are possible, within the scope of the invention, with reference to the drawings some of the presently preferred embodiments can be described.

As shown in FIG. 1, the casing cutting tool 10, referred to herein at times as cutting tool 10, comprises a main body 20, which carries multiple rotatably mounted blades 30 therein. For reference only, “uphole” and “downhole” directions are noted on FIG. 1 to note the typical orientation of casing cutting tool 10 in a wellbore. Cutting tool 10 has a longitudinal axis LA, shown in FIG. 1, running longitudinally through the center of the tool. A bore 22 runs longitudinally through casing cutting tool 10. Main body 20 preferably comprises a means for connecting casing cutting tool 10 to a drillstring, for example threaded connections or tool joints noted as TJ at each end.

Cutting tool 10 comprises a means for rotating blades 30 from a first, retracted position in which blades 30 are positioned within recesses 21 within main body 20; to a second, extended position (substantially at right angles to the first position), as can be seen in FIG. 1. Different mechanisms can be used to rotate blades 30 from a first, retracted position, generally within main body 20 and not protruding significantly therefrom; to a second, extended position, wherein blades 30 are partially or fully extended from the body, as seen in FIG. 1. In an exemplary embodiment, the means for rotating blades 30 between the first and second positions comprises, generally, a piston 23 disposed in bore 22, which can move longitudinally in response to fluid flow. Piston 23 has a bore 24 longitudinally through it. When fluid is pumped down the bore of the drillstring, through bore 22 of main body 20 and bore 24 of piston 23, piston 23 is forced in a downhole direction. A lower end of piston 23 bears against heel portions 23A of blades 30, forcing the heel portions downwardly and causing blades 30 to rotate to the position shown in FIG. 1. While not confining the current invention to any particular operating mechanism, one suitable mechanism for the means for rotating blades 30 is that disclosed in U.S. Pat. No. 7,063,155, owned by the assignee of this invention. Cutting tool 10 may comprise two, three, or more blades, although two blades may be the preferred number and are shown in FIG. 1. This permits blades 30 to be robust in dimensions and strength. FIG. 1 shows the blades rotated to their fully extended position, at roughly 90 degrees from the longitudinal axis of the tool.

As can be seen in FIG. 1, and in more detail in FIG. 2 and following figures, fixed to or near the outermost ends of blades 30, or integral to blades 30, are one or more cutters 40. As can be seen in the drawings, particularly FIGS. 2-5, rather than the more usual cutter geometry of a relatively small dimension in a longitudinal direction (uphole/downhole, with the cutters in an extended position), cutters 40 are elongated (when viewed radially) in a direction coincident with or slightly angled from the longitudinal axis of main body 20, for example having a cross section shape of an elongated rectangular shape, with a longer dimension in a direction generally aligned with the longitudinal axis of cutting tool 10; however, it is understood that cutters 40 are preferably angled somewhat from the longitudinal axis of cutting tool 10, as described in more detail below. It is understood that the view of blade 30 with cutters 40 mounted thereon, in FIG. 2A, is a view generally along the longitudinal axis of the tool (an end or “top view”). It is to be understood that the elongated cross section shape may be rectangular, oval, or some other elongated shape.

With regard to the number of cutters per blade, at least one cutter, preferably two or more, preferably three, are provided, as seen in FIGS. 2 and 3. It is understood that the scope of the invention encompasses any number of cutters. For example, one embodiment of the invention comprises only a single elongated cutter on each blade.

The cutters of the present invention comprise a number of structural attributes which increase the cutting efficiency of the tool, and extend the cutting life of the tool, and enable substantially higher rates of cutting than prior art tools. Said structural attributes include, but are not limited to, the following:

-   1. The cross section shape and dimensions of the cutters are     elongated, typically generally rectangular, with a longer dimension     generally axially aligned with the longitudinal axis of the tool     (although as described below, preferably cutters 40 are angled     slightly with respect to the longitudinal axis of cutting tool 10),     as in FIGS. 4 and 5. Preferably, the outermost corners 50 of cutters     40 are rounded, as shown in FIG. 6, in order to control penetration     through a casing wall. Preferably, the lower edge is not “flat” or     horizontal (with respect to the longitudinal axis of main body 20 of     the tool), but is downwardly angled, when moving in an outwardly     radial direction away from the main body of the tool; this is also     shown and annotated in FIG. 6. -   2. When viewed in a radial direction, FIG. 4, cutters 40 are     preferably angled (or inclined) slightly with respect to the     longitudinal axis of the tool, such that the non-cutting end of the     cutter leads the cutting end of the cutter, and is therefore angled     in the direction of rotation or cutting. In FIG. 4, the direction of     movement of the cutters is shown by the arrows, with the bottom edge     of the cutter being the cutting surface. While the amount of     inclination can be varied, angles of three to ten degrees from the     longitudinal axis of main body 20 are believed to be suitable, with     a range of seven to ten degrees from the longitudinal axis of main     body 20 providing an efficient cutting arrangement.

It is understood that should the tool be configured so as to cut in an upward or uphole direction, then the direction of angle or inclination would be reversed from that shown in FIG. 4.

Another embodiment of the cutters takes the form of a chevron, comprising two rows of cutters, as seen in FIG. 7. Here, a first row of cutters 44 are provided and angled for cutting in a downhole direction, and a second row of cutters 42 are provided and angled for cutting in an uphole direction.

-   3. The base material for the cutters is preferably a steel, forming     the face of cutters 40 into which shaped “buttons” 60 of hardened     cutting material, for example tungsten carbide, are placed (in the     face of the cutter), as described further below, to form the primary     cutting surface. The steel cutter base is intended to be worn away     as the cutters rotate on and cut the casing, thereby continually     exposing fresh tungsten carbide cutting surfaces. For clarity and     due to space limitations, not all of buttons 60 are annotated with     the element number 60. Preferably, the hardness of the metal base is     related to the hardness of the casing being cut; that is, a harder     base metal will be used in cutting harder grades of casing, in order     to extend the life of the cutters. -   4. The upper edge of cutters 40 may be covered with cutting     material, for example tungsten carbide material or hardened cutting     buttons, to form a cutting edge, to enable cutters 40 to cut through     and penetrate the casing wall. FIG. 6 shows the preferred placement     of the tungsten carbide material 70 on the upper edge of the cutters     40. -   5. Cutters 40 may be separate parts, fixed to the outer ends or     faces of blades 30 by welding or similar means well known in the     art; or alternatively cutters 40 may be integral with blades 30,     essentially blades 30 and cutters 40 formed from a single piece of     material. FIGS. 8 and 9 show one possible embodiment of an     integrally formed blade and cutter. In one embodiment, each of     blades 30 comprises only a single cutter 40 (whether integrally     formed with blade 30, or mounted to blade 30 by welding or the     like). -   6. As previously noted, in a preferred embodiment, a number of     hardened cutting buttons, for example tungsten carbide buttons, 60     are placed into cutters 40, by means well known in the art. The     geometry of the buttons, and the positioning of the buttons on the     cutters, can be described.     -   a. the individual buttons 60, seen in a side view, are         preferably tapering toward the rear of the button; that is, the         larger diameter is toward the face of the cutter, in the         direction of movement of the cutter. FIGS. 2A, 2B, 2D, and 2E,         along with other drawings, show an exemplary tapered profile.     -   b. when viewed end-on, as in FIGS. 2C and 5, the buttons can be         circular, or preferably comprise a multi-sided shape, such as         octagonal shape, as in FIG. 2F. It is also desired that the face         of the buttons comprise multiple depressions, rather than a         smooth face, as seen in FIG. 2F, with FIG. 2G being a         cross-section of an exemplary button showing multiple dimples in         the face of the buttons. These button face attributes contribute         toward a “chip breaker” design, where the metal shavings from         the casing string being cut are broken into small, discrete         pieces, which tend to simply fall down into the wellbore. There         is no need, nor desire, to circulate such chips to the surface,         hence fluids of low viscosity can be used during the cutting         procedure. This is in contrast to prior art casing cutting         tools, which tended to create very long unbroken metal shavings,         which in turn tended to aggregate together downhole in a mass         resembling everyday “steel wool.” Such masses of metal cuttings         could and did result in drill strings becoming stuck in the         hole. Operators would therefore try to lift these long metal         cuttings out of the wellbore with high viscosity fluids, which         in turn created other issues.     -   c. As is shown in the drawings, for example FIGS. 2C and 5, the         individual buttons are preferably arranged on the face of         cutters 40 in a staggered vertical alignment (with respect to a         direction parallel to the longitudinal axis of the tool), so as         to minimize any gaps in cutting coverage.     -   d. The hardened cutting buttons can be of various hard         materials, such as tungsten carbide, diamonds, synthetic         diamond, polycrystalline diamond compact or PDC, and may be         coated with titanium or similar materials to extend the life of         the cutters.

Method of Use of the Cutting Tool

An exemplary method of use of cutting tool 10 can now be described. A set of blades 30 with one or more cutters 40 attached to (or integral with) each blade 30 is selected with dimensions appropriate for the size casing that is to be cut. Cutting tool 10 is lowered to the desired depth within the casing string being cut, on a tubular string, commonly referred to as the drillstring or work string. Fluids are then pumped down the drillstring through cutting tool 10, which rotates the blades and cutters outwardly from the main body, under influence of the operating mechanism, as previously described, and into the position of FIG. 1. Cutters 40 contact the inner wall of the casing; more particularly, the uppermost corners of cutters 40 come into contact with the casing wall.

Rotation of cutting tool 10 is commenced, and cutters 40 (being pressed against the casing wall by the opening mechanism of the tool) start to cut into the wall of the casing. As the cutting progresses, blades 30 are able to gradually open further, until maximum extension of the blade/cutter combinations is achieved—that is, the blade/cutters are rotated fully out, as in FIGS. 1, 4 and 5.

If it is desired only to cut or sever the casing, then fluid flow can be stopped, at which time the blades/cutters retract into main body 20, and cutting tool 10 can be pulled from the well. If it is desired to cut a “window” in the casing, namely to remove an extended section of casing, for example 10 to 20 feet, then once the blades/cutters are fully extended, a desired weight (from the drill string) is applied to cutting tool 10 while rotating. As can be understood from FIGS. 4 and 5, the multiple cutters 40 bear against the casing surface or edge below the cutters, and cut the casing, thus forming the window. Field experimental use has showed that the configuration of the cutting surfaces of cutters 40, for example tungsten carbide buttons, particularly the non-smooth “chip breaker” face, results in relatively small chips of metal, rather than long, connected shavings. Such chips fall down within the wellbore and do not have to be lifted to the surface by the fluid stream, thereby permitting use of lower viscosity fluids. Further, the risk of downhole balling up of long metal shavings, and in turn sticking the drillstring, is eliminated.

Once the desired length of window has been cut, fluid flow is stopped, the blades/cutters retract into main body 20, and cutting tool 10 can be retrieved from the well.

As previously noted, the base metal of cutters 40 wears away during cutting, continuously exposing fresh cutting surfaces (tungsten carbide, hardened cutting buttons, etc.) to the casing surface being cut. It is believed that this is a key component in achieving the much long cutter life, and much higher casing cutting rates, than achieved by previous casing cutting tools. The elongation of cutters 40, in a direction generally aligned with the longitudinal axis of cutting tool 10, provides an extended cutting life before the cutter is completely worn away.

CONCLUSION

While the preceding description contains many specificities, it is to be understood that same are presented only to describe some of the presently preferred embodiments of the invention, and not by way of limitation. Changes can be made to various aspects of the invention, without departing from the scope thereof. For example, dimensions of the various components of cutting tool 10 can be varied to suit particular jobs; the number of blades 30 can be varied, to three or more; the number of cutters 40 per blade 30 can be varied, for example one, two, three or more cutters per blade; size and shape of cutters 40 can vary; the angle of cutters 40 with respect to the longitudinal axis of cutting tool 10 can be varied; the number, size, and placement of the hardened cutting buttons on cutters 40 can be varied; the configuration of the face surfaces of the hardened cutting buttons can be varied to provide the most efficient “chip breaker” shape for the application; and methods of use can be varied.

Therefore, the scope of the invention is to be determined not by the illustrative examples set forth above, but by the appended claims and their legal equivalents. 

I claim:
 1. A well bore casing cutting tool, comprising: a main body having a longitudinal axis therethrough and comprising a means for connecting said cutting tool to a drillstring; a plurality of blades rotatably attached to said main body, and rotatable between a first, retracted position and a second, extended position in which said blades are extended outwardly from said main body, said plurality of blades disposed about a circumference of said main body; a means for rotating said plurality of blades between said first and second positions; and one or more cutters on each of said plurality of blades, wherein each of said one or more cutters has an elongated cross section shape, with a longer dimension of said shape angled in a direction of desired rotation of said cutting tool and with respect to said longitudinal axis of said main body, each of said cutters comprising a hardened cutting surface.
 2. The cutting tool of claim 1, wherein each of said blades comprises two or more of said cutters.
 3. The cutting tool of claim 1, wherein each of said blades comprises three or more of said cutters.
 4. The cutting tool of claim 1, wherein said hardened cutting surface of each of said cutters comprises a tungsten carbide coating.
 5. The cutting tool of claim 1, wherein said hardened cutting surface of each of said cutters comprises a plurality of hardened cutting buttons.
 6. The cutting tool of claim 1, wherein each of said cutters is inclined with respect to said longitudinal axis of said main body of said tool by an angle of between 7 degrees and 10 degrees.
 7. The cutting tool of claim 6, wherein said cutters comprise a metal base softer than a casing string being cut, and a plurality of hardened cutting buttons affixed to said metal base.
 8. The cutting tool of claim 7, wherein a lower edge of said cutters is angled downward in a direction away from said main body of said cutting tool.
 9. A well bore casing cutting tool, comprising: a main body having a longitudinal axis therethrough and comprising a means for attachment to a drillstring; a plurality of blades rotatably attached to said main body, and rotatable between a first, retracted position and a second, extended position in which said blades are extended outwardly from said main body, said plurality of blades disposed about a circumference of said main body; a means for rotating said plurality of blades between said first and second positions; and a first row of two or more cutters on each of said plurality of blades, wherein each of said two or more cutters has an elongated generally rectangular cross section shape, with a longer dimension of said shape inclined in a direction of desired rotation of said cutting tool and at an angle to said longitudinal axis of said main body, each of said cutters comprising a metal base and a hardened cutting surface comprising a plurality of hardened cutting buttons affixed to a face of said cutters.
 10. The cutting tool of claim 9, wherein said cutters are integrally formed with said blades.
 11. The cutting tool of claim 9, wherein said buttons comprise a polygon cross section shape.
 12. The cutting tool of claim 11, wherein said buttons comprise a concave face.
 13. The cutting tool of claim 11, wherein said buttons comprise a face having a plurality of dimples therein.
 14. The cutting tool of claim 11, wherein said hardened cutting buttons comprise tungsten carbide.
 15. The cutting tool of claim 11, wherein said hardened cutting buttons comprise polycrystalline diamond compact buttons.
 16. The cutting tool of claim 11, wherein a lower edge of said cutters is angled downward in a direction away from said main body of said cutting tool.
 17. The cutting tool of claim 10, wherein said buttons comprise a polygon cross section shape.
 18. The cutting tool of claim 17, wherein said buttons comprise a concave face.
 19. The cutting tool of claim 17, wherein said buttons comprise a face having a plurality of dimples therein.
 20. The cutting tool of claim 17, wherein said hardened cutting buttons comprise tungsten carbide.
 21. The cutting tool of claim 17, wherein said hardened cutting buttons comprise polycrystalline diamond compact buttons.
 22. The cutting tool of claim 17, wherein a lower edge of said cutters is angled downward in a direction away from said main body of said cutting tool.
 23. The cutting tool of claim 11, further comprising a second row of two or more cutters on each of said plurality of blades, wherein each of said two or more cutters of said second row has an elongated generally rectangular cross section shape, with a longer dimension of said shape inclined in a direction opposite to said first row of said cutters and at an angle to said longitudinal axis of said main body, each of said second row of cutters comprising a metal base and a hardened cutting surface comprising a plurality of hardened cutting buttons affixed to a face of said cutters, whereby said second row of cutters is disposed to cut a casing surface positioned uphole of said second row of cutters. 